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There is a specific and terrifying difference between “never were” monsters and “are not anymore” monsters
“The thing that was not a deer” implies a creature which mimics a deer but imperfectly and the details which are wrong are what makes it terrifying
“The thing that was not a deer anymore” on the other hand implies a thing that USED to be a deer before it was somehow mutated, possessed, parasitically controlled or reanimated improperly and what makes THAT terrifying is the details that are still right and recognizable poking out of all the wrong and horrible malformations.
Shout out to early 80s horror for having their group of kids be actually enjoyable and make you care about if they die or not. Later on movies devolved into the most annoying group of shitheads you want to see hacked and slashed but in the earlier days there was some genuinely great character dynamics. (My bloody valentine, Prom night, Slumber party massacre.) now of corse remakes go on to absolutely ruin the praise I just gave but what can you do?